Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $89.53   6.491%   $95.3414   $95.34   $95.35   $95.30  
  Purchase #2 $184.65   7.222%   $197.9854   $197.99   $198.00   $198.00  
  Purchase #3 $34.66   10.804%   $38.4047   $38.40   $38.40   $38.40  
  Purchase #4 $28.76   5.838%   $30.439   $30.44   $30.45   $30.40  
  Purchase #5 $246.33   5.764%   $260.5285   $260.53   $260.55   $260.50  
  Purchase #6 $216.76   5.353%   $228.3632   $228.36   $228.35   $228.40  
  Purchase #7 $155.71   9.566%   $170.6052   $170.61   $170.60   $170.60  
  7 purchase totals = $956.40       $1,021.6674   $1,021.67   $1,021.70   $1,021.60